“EVALUATION OF NORMAL VARIANTS OF CIRCLE OF WILLIS AT MAGNETIC RESONANCE ANGIOGRAPHY”

Abstract Id: IRIA - 1023

The brain, though representing only 2% of the total body weight, receives one fifth of the resting cardiac output. This blood supply is carried by the two ICA and the two VA that anastomose at the base of the brain to form the “Circle of Willis” (COW).

The COW is divided into anterior and posterior circulation based on the part of brain supplied, the carotid arteries and their branches contribute the anterior circulation, while the vertebro-basilar system the posterior circulation.

With the advances in neurosurgery and the management of these intracranial arterial pathologies, the knowledge of the intracranial vascular anatomy is important which presents in individuals with several normal variations.

The anatomic relationships between bone and blood vessels are better delineated by high spatial resolution of (3D) multi-detector CTA, and are reported with a high sensitivity and specificity of 81%–90% and 93% respectively, however patient’s exposure to radiation and risks related with use of contrast agents are involved.

Previous studies have demonstrated that 3D-TOF MRA is a sensitive, non-invasive imaging modality suitable for evaluation of the COW in healthy volunteers and patients with carotid artery disease, and Chronic Kidney diseases.

INTRODUCTION:

The aim of the study is to evaluate the different anatomical variations of the Circle of Willis in local population, using magnetic resonance 3D-time of flight angiography.• To determine average vessel diameter.• To evaluate gender related differences.

AIMS & OBJECTIVES

.

INCLUSION CRITERIA

Patients referred to Radiodiagnosis department for MRI BRAIN.

Old data acquired from PACS (nova) / Work station, previously saved images.

Patients of all age groups and both gender who were considered as healthy subjects with regard to the anatomy of the COW.

EXCLUSION CRITERIA

Contraindications to MRI. Poor / Distorted image with

artefact. Images with Infarct,

Haemorrhage, Mass lesion, signs of ischemia.

Atherosclerosis / Narrowed Vessels with turbulent / low flow.

MATERIALS & METHODS :

All ages & Gender ( M & F )

• Anterior part of COW• Posterior part of COW• Others

NOVA PACS – MRA (3D –Tof )

MRI – BRAIN of patients following inclusion criteria

Variations in Circle of Willis

Vessel diameter

Gender

N = 503(M-

287, F-216)

COMMON VARIATIONS EVALUATED:

VARIATIONS INVOLVING ANTERIOR PART OF COW:

BA E G

C D H J

VARIATIONS INVOLVING POSTERIOR PART OF COW:

K L

M N

O P

Q R

S T

OTHER VARIATIONS INVOLVING COW:

A C

B B

D E

F G

RESULTS:

RESULTS ( Anterior / Posterior / Others ) :

RESULTS ( Vessel diameter ):

AN

TE

RIO

R C

OW

:8

Varia

nts

Typ

e A

: 52

.9%

Typ

e H

: 12

.7%

Typ

e f: N

il

PO

ST

ER

IOR

CO

W:

10

Varia

nts

Typ

e K

: 32

.8%

Typ

e o

: 31

.6%

Typ

e N

: 16

.1%

OT

HE

RS

: 7

Varia

nts

(6.2

%)

Fen

estra

tion

2.2

% P

TA

(type – 2

) 0

.6%

DISCUSSION:

N = 503 (M-287, F-216)

Mean age – 42yrs (1month – 82 yrs)

Vessel Diameter:

< 1 mm – hypoplasticMale > FemaleSig “P value”- ICA & Lt Pco ( male )Rt Pcoa ( in > 40 years )

Limitations:

• Single obserever• Vessel length

measurement • Specific age

group• Flow rate

measurement ( Phace contrast MRA)

CONCLUSION:

Based on the results and the methodology employed, we have concluded that: The morphological variations and diameter differences in the COW are common with gender or age related with significant prevalence as demonstrated in our study at asymptomatic persons. The non-invasiveness and sensitivity of 3D-TOF MRA is one of the best method for evaluation of these normal variants. Our findings show that configuration of the COW vary largely in general local population.

The prevalence of complete configuration of the circle is higher in younger persons as well as in females. And some of the vessel diameters show statistically significant differences according to the age and gender. This normal anatomical variant identification plays an important role in surgery.

The presence of bilateral PCOA is less commonly reported in

previous literatures, which is better appreciated on source image correlation with MIP image. Several other variants are possible. To our knowledge, there is no proper classification found for these variants. The present 3D-TOF MRA has a limited role in low flow vessels. In future studies these drawbacks can be overcome by the high resolution 3T MRI and correlation with phase contrast MRA.

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REFERENCES:

Thomas Willis (1621 -1673)

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